Field of the Invention
The subject invention is generally directed to exhaust systems for blowdown exhaust on blast pots and is specifically directed to a silencer for the exhaust system.
Discussion of the Prior Art
Blast pot systems are well known in the abrasive blasting industry wherein particulate abrasives are released under pressure against various surfaces in surface preparation applications. It has long been important to depressurize the pressure vessel or blast pot during times of non-use, for periodically replenishing the abrasive material in the vessel or for routine maintenance. The depressurization of blast pots involves first shutting down the system pressure and then releasing the pressure in the vessel through a port commonly referred to as a blowdown port. Typically, this generates a high volume of air and creates with it a loud noise level, sometimes as high as 130 dB, which is typical during the initial blowdown procedure. While it is not necessary to reduce this noise level, it is desirable to do so. In addition, particularly when the blast pot is full of particulate abrasive matter during blowdown, the exhausted air contains abrasive particles which can be destructive.
It is, therefore, desirable to reduce the level of noise and contain the destructive flow of particulate matter during blowdown.
Several systems have been designed to provide noise control. One design utilizes a small cylindrical porous element with external wire mesh reinforcement. All of which are encased in a metal housing with two slotted exhaust ports located 180 degrees from each other. The element can be replaced or cleaned by removing a pipe plug at the end. While this design does suppress noise, the porous element can accumulate dust and “clog”. In addition, the design is such that the abrasive particles that are entrained in the airstream will rebound off the pipe plug and destructively strike the element. In addition, because of the flow of the destructive particles this design inherently has a short life span in use. In order to prolong life, daily cleaning is require, which is not realistic in the working environment. As a result, end users will usually remove the system once it is damaged. A further drawback to this system is that the slotted port on the side of the housing will direct exhaust air and fugitive particles horizontally. This could blow dust and particles onto anyone near the exhaust.
In another system, the airflow is exhausted through a large porous (small pores) element encased by perforated metal. This design offers adequate noise suppression with good airflow. However, the design can trap dust and quickly become more restrictive.
Other examples offer the similar styles that place a porous type element or mesh in the direct or rebound path of the exhaust compressed air near the expansion point.
One such system is disclosed in my copending application Ser. No. 13/021,256, entitled: “Air Blast Blowdown Silencer System for Blast Pot”, entitled filed on Feb. 4, 2011. The blowdown system there disclosed includes an initial restrictor in communication with a blast pot vessel for controlling the flow of pressurized air from the vessel into a first expansion chamber which is in communication with a reducer. The outlet of the reducer introduced into a muffler system which includes an exhaust path and a deflector for absorbing and or deflecting abrasive particles which may be evacuated from the blast pot vessel during blowdown.
Decompressing or “blowing down” a blast pot without a muffler or silencer could create noise levels in excess of 130 dB. In addition, the grit particles that are often mixed and entrained within the exhaust flow are traveling at a high velocity. These particles will abrade any obstruction of the exhaust airstream. Prior art would use mufflers that direct all or most of the exhaust flow through porous membranes. While this does reduce the exhaust noise level, the membranes would eventually clog as they accumulate dust. The clogged membranes restrict air flow and progressively increase decompression time, creating a potentially hazardous situation.
In addition, these porous elements were not capable of withstanding impact and would wear quickly. The aforementioned patent application utilizes an expansion chamber and sound absorptive material to reduce the noise level. While this sufficiently mitigated the abrasion of exhaust air from the device, it did not address the abrasion on the sound absorptive components within.